Much development work has been done in connection with the design of tear-opening features for cartons, envelopes, and other forms of packages and containers. Highly advantageous forms of such devices are described and claimed in the above-mentioned related applications. In general, known tear-opening structures have comprised guide strip means, formed of relatively non-tearable materials, secured on the outside surface of a panel to be opened. The guide strip means typically is formed with a guiding edge, which can be an edge of the guide strip or the longitudinally extending line of weakness formed in the guide strip material. In either case, the guide strip effectively forms a cutting edge against which the wall of the container can be cleanly torn. Frequently, the guide strip means is arranged to form two spaced-apart guide edges, so that a thin, longitudinally extending strip of wall panel material can be cleanly torn away during the opening process.
Tear-opening devices of known construction typically employ a tear strip element, secured to the internal surface of the panel to be opened and which is generally aligned with the guide strip means mounted on the outer surface of the panel. An end of the tear strip element is accessible, enabling it to be pulled outward relative to the container panel, causing the panel to be torn longitudinally by a shearing action between the guide strip means mounted on the outer surface and the tear strip means mounted on the inner surface of the panel.
A wide variety of devices have been proposed for defining the guide strip means provided on the outside of the container wall. The most elementary of these is a single strip of material, or a pair of spaced apart strips, formed of relatively non-tearable material and adhered to the outer surface of the container wall. A more advantageous form of guide strip arrangement may comprise a pair of spaced-apart guide strip elements mounted on a common carrier strip formed of tearable material. Such an arrangement is disclosed in the Kim U.S. Pat. No. 5,035,328. The carrier strip serves to support and space the guide strip elements and thus facilitates their mounting on the container wall. A guide strip arrangement may also be provided in which a relatively wide, composite guide strip structure is provided, which is tearable longitudinally in any one of a plurality of locations, while being highly resistant to tearing in the transverse direction. The longitudinal tearability of the structure may be provided by incorporating a substantial number of narrow, longitudinally extending elements, by utilizing available plastic materials having unidirectional tearing characteristics and/or by providing multiple longitudinally extending tear lines in otherwise relatively tear-resistant material. With guide strip structures of the type described, a tear strip of narrower width dimensions than the guide strip structure may be located anywhere between the edges of the structure. When the tear strip is drawn outwardly, guide strip edges are automatically formed by rupturing of the guide strip structure along longitudinal tear lines.
Although the structures described above are functionally advantageous and serve well to perform the container-opening functions for which they were designed, they can in some instances inconvenience the container manufacturing process, because of the need to use a variety of materials in forming the guide strip and tear strip elements, and the need for the exercise of care in the relative alignment of the guide strip materials, on the outside of the container wall, with the tear strip elements, on the inside of the container wall.
Pursuant to the present invention, a novel and improved arrangement is provided which significantly simplifies the process of manufacturing containers with tear strip opening devices without in any way compromising the performance of the tear-opening feature. Indeed, performance of the tear-opening feature is, if anything, enhanced. More specifically, the device of the invention incorporates a uniquely advantageous form of double guide strip construction in which separate guide strips are mounted directly opposite each other on the outside and inside surfaces of the container wall to be opened. Pursuant to the invention, the guide strip mounted on the outside surface of the panel effectively constitutes a guide edge-forming means, while the guide strip, mounted in directly opposing relation on the inside surface of the panel, constitutes a tear strip means. Two important advantages are derived from this arrangement: First, a similar (typically identical)--dual purpose guide strip serves both functions, of providing a guide edge-forming means and a tear strip means respectively on the outside and inside surfaces of the panel. Thus, a single component can serve both purposes, whereas with conventional structures, one type of material serves to provide a guide strip means, and a different type of material provides a tear strip means. A second significant advantage to be derived from the invention is the facility of accurately aligning the guide edge means, on the outside surface of the panel, with the tear strip means, on the inside surface.
The device of the invention accommodates a wide variety of guide strip constructions structures which, when mounted on opposed surfaces of a container panel, provide a uniquely advantageous double strip opening device.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention, and to the accompanying drawing.